Electric cables often are installed in hazardous or corrosive environments. Such cables employ a core of circular diameter which is covered by an external metallic sheath used as a protective member. These sheaths provide an impervious metallic envelope capable of preventing entry of humidity and resisting corrosion caused for example by moisture, acids, gases and the like. Conventionally, such sheaths are formed from aluminum or aluminum-manganese alloys. These sheaths form a protective envelope. The thickness of the sheath depends in part upon the size of the core diameter and increases with increasing size.
The installation of the sheath about the core utilizes strips of aluminum metals or alloys which are formed around outer surface of the core of the cable and then are longitudinally welded and corrugated.
However, cables utilizing metallic sheaths, as for example heavy power cables, are normally manufactured in long lengths and are wound on reels. For cores of larger diameter employing thicker sheaths, the weight of the upper layers of sheathed cables causes the upper layers to crush downward against the lower cable layers, often causing some deformation of the sheath and core in the lower cable layers. This deformation creates problems in subsequent manufacturing steps such as jacket extrusion, cable termination and also in final installation in cable ducts. In addition, the cost of the sheath material increases substantially as the sheath thickness is increased.
The present invention is directed toward a metallic sheath which retains sufficient crush resistance to overcome the deformation problem while at the same time exhibiting a reduction in the sheath thickness which provides substantial reduction in the amount and cost of sheath material.